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Lesson plan Grade 7 Engineering & Design

Corvid Hollow Rain Garden: Defining Design Criteria and Constraints

A 50-minute grade 7 lesson where students separate design criteria from constraints for a school rain garden and calculate the runoff volume it must capture.

Objectives

  1. Students will define specific, measurable criteria and constraints for a stormwater design problem.
  2. Students will calculate the volume of roof runoff a rain garden must capture using a given conversion rate.

Vocabulary

Rain garden
A rain garden is a shallow planted dip in the ground that catches rain running off a roof or driveway and lets it soak slowly into the soil. Its deep-rooted plants help clean the water.
Impervious surface
An impervious surface is any hard surface, like a road, roof, or parking lot, that rain cannot soak through. The more impervious surface a town has, the more stormwater rushes off it.

Also: criteria, constraint, runoff

Teacher overview

Corvid Hollow Middle School, a fictional school used in this lesson, has a low spot in its courtyard that floods every time it rains hard, because runoff from the flat gym roof has nowhere to go but across the pavement. This lesson asks students to act as the engineering team studying that problem: before they sketch any rain garden design, they must write down exactly what the design has to achieve (its criteria) and exactly what limits it (its constraints), then calculate how much water the garden actually needs to hold. A common misconception in this lesson is that students treat "make it bigger" as a solution to every design problem; the procedure is built to show that a good criterion is a specific, measurable target, not an instruction to add more material.

Procedure

Hook (5 min): Describe the flooded corner of the Corvid Hollow courtyard and ask students what "the problem" actually is. Collect a few guesses on the board without judging them; most will describe symptoms ("it gets muddy") rather than a stated, measurable problem.

Direct instruction (10 min): Introduce the terms criterion (something the design must achieve, stated as a target) and constraint (a limit that bounds the design, such as space, materials, or time). Present the site fact: the gym roof is a flat, impervious surface of 3,000 square feet. Introduce the school's runoff rule, which converts roof area and rainfall into gallons: roof area (square feet) times rainfall (inches) times 0.623 equals gallons of runoff. Model computing the capture target for a 1-inch storm: 3,000 × 1 × 0.623 = 1,869 gallons. State this number aloud as an example of a criterion: "the rain garden must be able to hold at least 1,869 gallons after a 1-inch storm."

Guided practice (15 min): As a class, list at least three constraints for the Corvid Hollow rain garden alongside the capture-volume criterion: the garden's footprint cannot exceed the fenced planting bed near the gym, it must use plants that survive both standing water and dry spells, and it must drain within about a day so it does not become a mosquito breeding site. Discuss why each of these limits the design without describing how to meet it. Then, as a group, work the first student calculation. Question 1: Using the same runoff rule, find the capture target for the school's cafeteria roof, which measures 1,800 square feet, for the same 1-inch storm.

Independent practice (15 min): In teams of two or three, students record design criteria on chart paper for a third building at Corvid Hollow, the science wing, which has a roof of 2,400 square feet. Question 2: Calculate the 1-inch-storm capture target for the science wing roof. Teams also write three original constraints of their own (not copied from the guided example) that a real design team would need to respect.

Closure / exit ticket (5 min): Each student answers Question 3 on an index card: "The library roof at Corvid Hollow is 1,200 square feet. Using the same storm (1 inch of rain) and the school's runoff rule, how many gallons must its rain garden be able to capture?" Collect the cards and scan for the correct method (multiplying by 0.623) before dismissal.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

The gym roof is the worked example modeled during direct instruction, not a question students solve: 3,000 sq ft × 1 in × 0.623 = 1,869 gallons. The three questions students answer themselves are keyed below, numbered to match the procedure.

  1. Answer: 1,121 gallons. Cafeteria roof (guided practice, Question 1): 1,800 sq ft × 1 in × 0.623 = 1,121.4 gallons, which rounds to 1,121 gallons.
  2. Answer: 1,495 gallons. Science wing roof (independent practice, Question 2): 2,400 sq ft × 1 in × 0.623 = 1,495.2 gallons, which rounds to 1,495 gallons. Accept any three original, non-copied constraints that genuinely limit the design (space, plant survival, drainage time, disruption to recess space, and similar).
  3. Exit ticket answer: 748 gallons. Library roof (Question 3): 1,200 sq ft × 1 in × 0.623 = 747.6 gallons, which rounds to 748 gallons.

Differentiation

Support

Provide the runoff rule already written as a fill-in equation ("___ sq ft × ___ in × 0.623 = ___ gallons") with the roof area and rainfall depth pre-filled, so students only complete the multiplication step. Allow a calculator for every calculation in this lesson.

Extension

Ask students to calculate, using only the teacher-provided rule, how much runoff the science wing roof would produce in a heavier 2-inch storm instead of a 1-inch storm, and to explain in writing whether the original capture-volume criterion would still be enough.

ELL supports

Pre-teach "criterion," "constraint," "runoff," and "impervious" with a simple visual: a photo or sketch of the flat gym roof with arrows showing water flowing off it onto pavement. Provide a sentence frame for the exit ticket: "The rain garden must hold at least ___ gallons because the roof is ___ square feet."